Property and Equipment, Net of Accumulated Depreciation (Components of Property and Equipment, at Cost) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Nov. 30, 2016	Nov. 30, 2015	Nov. 30, 2016	Nov. 30, 2015	May 31, 2016
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	$ 1,024.9		$ 1,024.9		$ 1,012.2
Less: Accumulated depreciation	675.6		675.6		659.2
Property and equipment, net of accumulated depreciation	349.3		349.3		353.0
Depreciation expense	25.5	$ 24.7	50.8	$ 48.7
Land and Improvements [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	8.3		8.3		8.3
Buildings and Improvements [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	103.1		103.1		103.0
Data Processing Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	197.9		197.9		196.1
Software [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	468.0		468.0		447.5
Furniture, Fixtures, and Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	113.7		113.7		125.0
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	109.0		109.0		108.2
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	$ 24.9		$ 24.9		$ 24.1